Surgical access procedures utilizing relatively large diameter catheters or cannula are well known in the art. Generally, the prior art access devices are formed as thin walled tubular members having a distal end which is inserted through the skin of the patient and a proximal or extracorporeal end which remains outside the patient's body and is configured to receive a variety of devices including valves, seal structures, additional catheters and surgical throughput devices for performing specific procedures at the distal end of the access device.
The traditional access procedure for positioning these relatively large diameter access devices is the guide-wire technique of S. I. Seldinger as described in BR. J. 2(6026): 21-22,#3 July 1976. Briefly, to insert the access device an appropriate area on the skin is identified and prepared for percutaneous puncture then a small diameter needle of sufficient length is introduced through the skin and underlying tissue into the target. A thin, flexible guide wire is inserted through the needle into the target cavity or blood vessel after which the small bore needle is withdrawn over the guide wire leaving the guide wire in the cavity. Using the wire as a guide tapered dilators or progressively larger dilators can be introduced through the outer tissues of the patient until an access channel having the desired diametric size is achieved. The last dilator serves as a guide for the final element of surgical access, a relatively large diameter access tube or introducer. Typically, an assembly of the tubular introducer with a cylindrical dilator extending through the lumen or bore of the introducer is slipped over the guide wire and manipulated into position within the target internal body cavity or blood vessel. After final placement the dilator and the guide wire are removed leaving the access device in position to receive and guide various surgical throughput devices and catheters through the access device into the target area for surgical operation.
To facilitate the manipulation and placement of traditional surgical access devices the devices are provided with a circular cross-sectional configuration. As a result, it is possible to introduce the circular cross section dilators and access tubes into and through tissue by sliding the assemblies over a cylindrical needle or guide wire which allows rotation of the device during the insertion procedure. Rotation about the guide wire axis reduces longitudinal friction as the assembly is pushed through tissue during its introduction. This ability to rotate the round cross section dilator or introducer access device assemblies of the prior art, coupled with their relative rigidity allows the implanting specialist to effectively guide the devices around and through internal organs and other structures to position the working end of the introducer within the target site.
Following removal of the circular dilator the large diameter tubular introducer allows the surgical operator to conduct the desired surgical procedure utilizing a variety of channels and throughput devices which are introduced to the target site through the access device. Because these smaller cannulas, channels and throughput devices vary in number and size depending on the surgical procedure performed, the general tendency has been to combine several channels into a catheter of circular cross section which easily slides through the circular cross section of the introducer. For example, fiber optic bundles, surgical cutting devices, guide wires and cylindrical catheters for aspiration of cut tissue fragments can be put through the access devices to perform sophisticated internal surgical procedures with relatively minor trauma to the patient's skin, musculature and other surrounding tissue.
Early attempts at further reducing the trauma associated with prior art access devices relied upon thin wall construction utilizing elastomeric materials. However, access devices formed of these materials possessed a tendency to buckle or fold during insertion. More recently, an adjustable vascular introducer. for balloon valvulopasty was reported in Cardiovasc. Intervent. Radiol. (1989) 2:169-171 formed of a rolled up plastic sheet in tube form surrounded by a coaxial elastic sheath. This device would expand around the oversized portion of a balloon catheter as it passed through the device. Though apparently successful at overcoming the problems of buckling and folding, the construction of this adjustable introducer provided it with an expandable circular cross section of limited applicability beyond balloon valvulopasty.
Moreover, while a circular cross section access device may be preferable for the insertion procedure itself, the resultant circular cross section of the introducer is not always the smallest, least traumatic, or optimum cross-sectional configuration for conducting the subsequent surgical procedure. Depending upon the number and type of throughput devices necessary to perform the intended surgical procedure, an ellipsoidal, figure-eight, triangular, or other non-circular cross section would result in more favorable access and require a smaller, less traumatic dilation diameter.
Accordingly, one of the objects of the present invention is to provide a surgical access device or introducer having optimized cross-sectional geometry for both insertion of the device and for post-insertion surgical procedures.
It is an additional object of the present invention to provide an access device having a variable cross section which, following insertion of the device, can be modified to an optimized cross-sectional size and shape depending upon the intended surgical procedure to be conducted through the access device.
It is an additional object of the present invention to provide an access device having a variable cross section which can be manufactured utilizing simple and inexpensive materials and techniques.